Non-cat efficiency question

[mike01]

If you wanted to get the most heat out of your wood with a modern non-cat stove without any other considerations (such as burn or coal time), would you:

a) fully load the stove and reduce the air to get a slow burn

or

b) put in only a few splits, maybe 2 or 3, and burn wide open or close to it, ensuring maximum secondary combustion

?

 

[rdust]

My non cat I always tried to burn in cycles, it seemed to work best for me.

Just a note, burning a non cat wide open doesn't get you maximum secondary combustion, as you close the primary air down you'll pull more secondary air in.

 

[mike01]

I could be wrong, I'm pretty new to this, but it seems to me that you need primary air to maintain secondary combustion, not just secondary air. If I get an awesome blazing fire with massive secondary combustion in the 600F range and then shut down primary air, the secondary combustion dies fairly quickly, but if I keep the primary air about half way to one quarter open I can maintain secondary combustion for hours. That seems, logically, like it should be a more efficient fire.

 

[Stump_Branch]

Mike, non cats are best run by decreasing the primary air (most secondary air is uncontrollable) in stages.

For an efficent long burn, load up full on a established bed of coals. Then back the air down say...under 25% At a time. let it sit for say...10 to 20 minutes at each stage. These amounts will vary with the stove, wood, chimney, weather and of course the end user. But you get the idea.

Maybe some stoves and setups you can shut the air down 100%. Mine was/is always a game as to how far i can shut the air, get the most heat, while burning clean, and last a good while at the same time.

 

[Ash_403]

I could be wrong, I'm pretty new to this, but it seems to me that you need primary air to maintain secondary combustion, not just secondary air. If I get an awesome blazing fire with massive secondary combustion in the 600F range and then shut down primary air, the secondary combustion dies fairly quickly, but if I keep the primary air about half way to one quarter open I can maintain secondary combustion for hours. That seems, logically, like it should be a more efficient fire.

You are describing my Regency I3100 also. This is the 3rd winter I've had it. That is the norm for me too.

 

[Lumber-Jack]

I'm sure when it comes to setting the draft a lot depends on the particular stove and the type of wood and how dry it is.
With my Regency F2400 and the dry wood I have, if I don't shut the draft down completely after the secondarys start my stove will get too hot.

 

[Swedishchef]

Some stoves react differently than others. In mine I get the stove cranking for 5-6 minutes. I then turn it down to about 25% air intake for another 2-3 minutes and then down to 10-15% for the remainder of the burn. If you cut off the primary air too fast, the stove won't have time to begin pulling more air in via secondary tubes and you usually end up choking the fire (on mine anyways...). That is why you have to do it in stages. The principle is that inside the stove a strong draft is created (air going into the stove and then out the chimney). Cutting down the primary air forces more air through the secondaries to compensate. Some stoves require the primary to remain open a bit as the secondaries don't provide enough oxygen for continuous combustion.

That's my 2 cents...lol

Andrew

 

[rdust]

I could be wrong, I'm pretty new to this, but it seems to me that you need primary air to maintain secondary combustion, not just secondary air. If I get an awesome blazing fire with massive secondary combustion in the 600F range and then shut down primary air, the secondary combustion dies fairly quickly, but if I keep the primary air about half way to one quarter open I can maintain secondary combustion for hours. That seems, logically, like it should be a more efficient fire.

Half way to a quarter open is different than the "wide open or close to it" that you posted in your first post. Every set up/stove runs different. Typically one of the EPA non cat stoves, a chimney with a good draft and seasoned wood you can dial the the primary down to 25% or less and maintain strong secondaries after the fire is established. As primary air is slowly closed down this will cause the stove to draw more secondary air into the stove and allow the heat to stay in the stove longer instead of sending it up the chimney. Most non cats also do not allow you to fully close the primary air, of course every stove is different so yours may close completely.

My non cat burned a little different with every load so I adjusted accordingly to each load. Sometimes I could close it down, sometimes I couldn't, I gave it what it wanted to burn clean and maintain a nice burn.

 

[mike01]

What you quoted was in reply to a specific statement. What I mean in the intial post is that if you burn two or three small splits you can leave the air much more open than if you load it to capacity and get a more active burn without risk of overfiring. My quesiton was, is such an active burn more or less efficient than a slower, less vibrant burn with a fully loaded stove and the air shut down as much as it will allow.

 

[Wood Duck]

I think as long as there is enough air - primary or secondary - to fully burn all of the gases and smoke then the less air the better. The peak efficiency should be at the point where there is complete combustion with minimum air. Getting heat from the wood into your house has two parts, completely burning the wood and all its gases and smoke, and keeping that heat in the house rather than blowing it up the flue. It seems like with a big load you can set the primary air lower and therefore it seems like big fires would be more efficient.

 

[Stump_Branch]

What you quoted was in reply to a specific statement. What I mean in the intial post is that if you burn two or three small splits you can leave the air much more open than if you load it to capacity and get a more active burn without risk of overfiring. My quesiton was, is such an active burn more or less efficient than a slower, less vibrant burn with a fully loaded stove and the air shut down as much as it will allow.

Is there smoke coming from the stack? That would be the best litmus test. If three logs and active fire makes no smoke, makes X amount if heat over Y amount of time better than a full slow fire, then sure more efficient.

I think folks are saying in the end the longest highest heat output burn is best. Yes most try to fill the stove to enhance the length portion of that.

My vogelzang insert i had was a three log queen. Anything more and the burn suffered. Each stove, each situation, each user, results will vary.

 

[stoveguy2esw]

the thing to remember with a non-cat is that you do after a fashion have some control over secondary air. remember this, a chimney will pull "X" air at a certain stack temp, now when you have the primary air "P" wide open then secondary air "S" is reduced due to more ease in pulling the primary in most cases, stoves are designed for this to happen.

so as you close the primary the ratio of air split between "P" and "S" is slanted to the "S" side, but the flue is still pulling "X"

essentially X=P+S the "balance" is changed as the primary is closed, this denies easy primary air so with "X" still in effect the "S" increases

now with a smaller load one should remember that the velocity of the air in the firebox is diminished somewhat by the larger open airspace from less fuel being present so the consumption will be a bit slower per cubic unit of measure unless the primary air is increased to speed this air up earlier in the fire. this may be needed to gain enough heat in the secondary zone of the firebox to achieve lightoff of secondaries. also holding enough primary heat when draft is reduced can be tricky as well.

in short its hard to get the max efficiency in burning with a short load when compared to a full load

 

[mike01]

I did not know that...thanks!

For me it is much easier to get good secondaries with a small fire though. Why is that? For example, yeterday I burned two fires with the same kind of wood, both on an existing coal bed. In one I put in three splits criss crossed and had a good fire in minutes (maybe 10 minutes or less before lowering "P") with good secondaries. Later on after that fire turned to coals in about 3 hours, I started another one with the stove almost loaded to capacity, logs north shouth, and it took about 40 minutes or longer to get a good fire and the secondaries did not want to stay lit and I had to mess with "P" a bit before being able to leave it alone.

Was it airflow? Better airflow over the crisscrossed logs?

 

[stoveguy2esw]

i guess it depends on if its a reload or starting from a cold unit. with coals you already have a reasonable amount of heat, now with a "crisscross" load you expose a lot of surface area of the splits to the air flowing through the stove so they will burn faster than if they are stacked tightly together.

the "airflow" is simply the air pulled through the firebox by the chimney's draft, now the amount of open space this air has to move through can have an effect on the speed at which it passes through the space, this is why loading a full load can increase velocity through the firebox unless its loaded so tight that there is not enough open air space to allow that much air to flow freely.